The main rotor of a rotary-wing aircraft, in particular a helicopter, is generally rather large, which makes it difficult to save space on a parking area, or on the deck of a ship for an on-board helicopter, or indeed when stored in a hangar. To reduce this size, a helicopter is typically fitted with a main rotor in which each blade can be folded back.
Nevertheless, each blade is secured to the rotor mast via a member generally known as a link sleeve fixed to an element of the rotor mast known as the hub. The sleeve is itself connected to the hub by retaining-and-hinge means enabling the blade to perform angular motion in pitch, in flapping, and in drag as required for proper operation of the main rotor assembly.
In contrast, when the blades are being folded back, such angular motion, and in particular the pitch motion must be inhibited.
Otherwise, the blade and its sleeve tilts about the pitch-changing axis of the blade, constituting a swinging mass. Such tilting can be dangerous for personnel in the vicinity of the helicopter and for the corresponding blade retaining-and-hinge means which can be damaged. In addition, it is necessary to lock blade pitch in order to be able to perform repeated folding operations with the necessary accuracy.
Furthermore, gusts of wind or motion of the ship on which the helicopter is located can cause said swinging masses to move, thereby running the risk of damaging the component parts of the rotor, and this can also be dangerous for personnel.
Solutions have already been proposed for mitigating those drawbacks. In those solutions, pitch locking is obtained by disconnecting all of the pitch links from the pitch levers, giving rise, amongst other things, to the pitch setting of the blades being taken out of adjustment. Proposals have also made in French patent application FR-96/12817 filed in the name of the Applicant to lock the swash plate relative to the hub by means of tooling links.